After several hours of mindnumbing wipes and a bucketful of Phantom and/or Dragoon excretions shoved down my throat, I managed to drag this kit all the way to the extraction with a decent time:
Quarksman:
16:32 | M-99 Saber | Glacier | Cerberus | PC | Alquinn
As is customary when the time is good, shooting is nothing spectacular.
In retrospect, I probably should've taken the evolution 4a of Marksman, since the reticle bloom is pretty significant and firing at maximum speed makes all the shots following the first one rather inaccurate. As result of that, I often slowed down shooting in favour of higher accuracy.
Protip: with this setup it is, in fact, quite efficient to prioritize killing Assault Troopers during early waves (priority order being Guardian>Assault Trooper>Nemesis>Centurion).